简介:Thehyperpolarization-activatedcurrent(If)playsanimportantroleindeterminingthespontaneousrateofcardiacpacemakercells.Theautomaticrhythmicityalsoexistsinworkingcellsofembryonicheart,thereforewestudieddevelopmentalchangesinfunctionalexpressionandβ-adrenergicregulationofIfinembryonicmouseheart.TheexpressionofIfishighinearlydevelopmentalstage(EDS)(10.5daftercoitus)ventricularmyocytes,lowinintermediatedevelopmentalstage(IDS)(13.5d)atrialorventricularmyocytesandevenlowerinlatedevelopmentalstage(LDS)(16.5d)atrialorventricularmyocytes,indicatingthatthesecellsoftheEDSembryonichearthavesomepropertiesofpacemakercells.β-adrenergicagonistisoproterenol(ISO)stimulatesIfinLDSbutnotinEDScardiomyocytes,indicatingthattheβ-adrenergicregulationofIfisnotmatureinEDSembryonicheart.Butforskolin(adirectactivatorofadenylatecyclase)and8-Br-cAMP(amembrane-permeableanalogueofcAMP)increasetheamplitudeofIfinEDScells,indicatingthatadenylatecyclaseandcAMPfunctionfairlywellatearlystageofdevelopment.Furthermore,theresultsdemonstratethatIfismodulatedbyphosphorylationviacAMPdependentPKAbothinEDSandLDScells.